1. Field of the Invention
This invention relates to an image forming apparatus such as a copying machine or a printer of the electrophotographic type, the electrostatic recording type or like type in which a developer is made to adhere to a latent image formed on an image bearing member to thereby visualize the latent image, and particularly to an image forming apparatus using a two-component developer including a toner and a carrier as a developer, and provided with a toner replenishing device for replenishing with the toner.
2. Description of Related Art
FIG. 13 of the accompanying drawings schematically shows the cross-sectional construction of an example of a developing device using a two-component developer including a toner and a carrier as a developer. FIG. 14 of the accompanying drawings shows the developing device of FIG. 13 as it is seen from above it.
In this example, the developing device 2 is provided with a developing container 10, and a developing sleeve 2A as a developer carrying member is provided in the opening portion thereof opposed to an image bearing member 1. A magnet roller 3 as magnetic field generating means is fixedly disposed in the developing sleeve 2A.
A screw 5 and B screw 6 as carrying and agitating means for carrying the developer to the developing sleeve 2A are disposed in the developing container 10. The A screw 5 and the B screw 6 are disposed substantially parallel to each other, and an inner wall 7 for partitioning the space between the A screw 5 and the B screw 6 is provided so that the developer may not come and go therebetween.
As will be understood from FIG. 14, the inner wall 7 is absent at the lengthwisely opposite end portions so that the developer can come and go between the A and B screws 5 and 6. The A screw 5 and the B screw 6 are adapted to carry the developer in opposite directions.
The developing sleeve 2A and the A screw 5 and the B screw 6 are connected together by gears (not shown) or the like, and when the developing sleeve 2A, the A screw 5 and the B screw 6 are rotated in the directions of arrows, the developer is uninterruptedly circulated therein as indicated by arrows in FIG. 14.
An inductance sensor 12 which is toner density detecting means is installed in proximity to the B screws 6. The two-component developer is basically comprised of a nonmagnetic toner and a carrier having magnetism, and the magnetic permeability of the developer is determined by the amount of carrier occupying a predetermined volume. Therefore, the inductance sensor 12 is installed to measure the magnetic permeability of the developer to thereby measure the ratio between the toner and the carrier (hereinafter referred to as the xe2x80x9ctoner densityxe2x80x9d).
Above the developing container 10 of the developing device 2, there is installed a toner replenishing device 9 for replenishing with a necessary amount of toner. A toner replenishing port 8 is located a little downstream of the inductance sensor 12, and when the toner is used for image formation and the toner density in the developer lowers, the amount of lowering of the toner density is measured when the developer passes the inductance sensor 12, and the developing container 10 is replenished with the necessary amount of toner from the toner replenishing device 9 through the toner replenishing port 8 and thus, the toner density in the developer is always kept constant.
As the toner density detecting means 12, use may be made of one of the optical density detection type, besides the inductance sensor described herein.
In a new developing device 2, there is prepared a standard developer adjusted in advance to predetermined toner density. When the new developing device 2 is set in an image forming apparatus, the agitating means 5 and 6 are rotated for a predetermined time and the developer uniformly pervades over the A screw 5 and the B screw 6 and the circulation of the developer becomes steady and the charged amount of the toner becomes settled. In this state, the measurement of the toner density is effected by the toner density detecting means 12. The value measured at this time is stored in a storing device (e.g. an EP-ROM free to write in or the like) mounted on the developing device, and is defined as a toner density reference value T inherent to this developing device.
During the control of the toner density during the printing operation, the difference between the measured value S and the aforementioned reference value T is compared, whereby it is possible to know How much the current toner density deviates as compared with the toner density of the standard developer and therefore, the amount of toner to replenish with can be calculated. By endowing the developing device with the toner density reference value T inherent to the developing device correspondingly to the developing device, toner density control optimum for each developing device 2 can be effected.
When the toner replenishment by the toner replenishing device 9 stagnates and the measured value S lowers and reaches a preset predetermined value (hereinafter referred to as the xe2x80x9climit value Lxe2x80x9d), it is judged that the developing device is not being replenished with the toner from the toner replenishing device 9, and the image forming apparatus is stopped and the supply of the toner to the toner replenishing device 9 is demanded.
In the above-described construction, however, the following problem has sometimes arisen with respect to the setting of the limit value L.
FIG. 12 of the accompanying drawings is an illustration showing an example of the transition of the measured value S, and the axis of abscissas indicates the number of prints and the axis of ordinates indicates the measured value S of the toner density.
During ordinary use, toner density control is effected so that the measured value S may converge around the vicinity of the reference value T. However, if high coverage images such as solid images are continuously printed, the toner in the developing device 2 will be rapidly consumed and therefore, the measured value S temporarily sharply lowers (Smin). Accordingly, unless the limit value L is set to a low level with a certain degree of safety rate foreseen with respect to Smin, the limit value L will be unexpectedly exceeded during the continuation of high coverage images or the like, and in spite of the presence of the toner in the toner replenishing device 9, the absence of the toner may be judged by mistake and the image forming apparatus may be stopped.
If in order to avoid such wrong detection, the limit value L is set to low developer density with the safety rate sufficiently given, the developer density will now become considerably low before the measured value S reaches the limit value L and therefore, the lowering of image density will occur and good images cannot be ensured. Also, image formation and agitation or the like are effected in a state in which the toner is little, namely, a carrier-rich state and therefore, the deterioration of the carrier progresses, and when the toner replenishing device 9 is replenished with the toner, if toner replenishment is effected at a stretch, fogged images may occur. If as described above, the limit value L is set too high, the possibility of effecting wrong detection will increase, and if the limit value L is set too low, the possibility of causing an inconvenience to images or the developing device will increase and therefore it has been very difficult to optimally set the limit value by the conventional construction.
Also, a single limit value L has always been used and therefore, it can be judged that the developing device is in a state in which it is not replenished with the toner from the toner replenishing device 9, but is has been impossible to discriminate whether it is the absence of the toner in the developing container 10, or the trouble of the toner replenishing device 9 (such as the badness of the toner discharging screws, the dogging of the replenishing port or the bad transmission by the gears) or the wrong detection in which the limit value L has been unexpectedly exceeded as during the continuation of high coverage images.
Accordingly, it is an object of the present invention to provide an image forming apparatus in which the detection of the absence of a toner in a toner replenishing device provided in a developing device is effected highly accurately and which is free of poor images and bad detection.
The above object is achieved by the image forming apparatus according to the present invention. Summing up, the present invention is an image forming apparatus provided with at least one developing device having a developing container for containing therein a developer including a toner and a carrier, means for detecting the density of the developer in the developing container, and a toner replenishing device provided with a toner container containing the toner therein and for replenishing the developing container with a proper amount of the toner in the toner container, wherein the absence of the toner in the toner container is judged by the density of the developer in the developing container becoming smaller than a predetermined limit value (L), characterized by remaining amount detecting means for detecting the remaining amount of toner in the toner container, and informing means for generating a signal indicative of a small remaining amount of toner when the remaining amount of toner in the toner container has become equal to or less than a predetermined amount, and in that the limit value (L) is effective only in a state in which the signal indicative of a small remaining amount of toner is being outputted.
The present invention adopts the above-described construction, whereby before the toner replenishing device outputs the remaining amount detection signal, even if the measured value S is below the limit value L, the absence of the toner is not judged and therefore, even if the density of the developer in the developing device is temporarily sharply lowered by the continuous printing of high density images or the like, such wrong detection that in spite of the presence of the toner in the toner replenishing device, the absence of the toner is judged by mistake can be prevented. Also, design is made such that the limit value L is made effective for the first time only after the toner replenishing device has outputted the remaining amount detection signal and therefore, it becomes possible to set the limit value L a little high, and the lowering of image density and the deterioration of the carrier due to the density of the developer having become too low can be prevented beforehand, and good images can be ensured till the last moment when the toner in the toner replenishing device becomes absent.
As described above, according to the present invention, an image forming apparatus provided with at least one developing device having a developing container for containing therein a developer including a toner and a carrier, means for detecting the density of the developer in the developing container, and a toner replenishing device provided with a toner container containing the toner therein, and for replenishing the developing container with a proper amount of the toner in the toner container, wherein the absence of the toner in the toner container is judged by the density of the developer in the developing container becoming smaller than a predetermined limit value (L), has remaining amount detecting means for detecting the remaining amount of toner in the toner container, and informing means for generating a signal indicative of a small remaining amount of toner when the remaining amount of toner in the toner container has become equal to or less than a predetermined amount, and is designed such that the limit value (L) is made effective only in a state in which the signal indicative of a small remaining amount of toner is being outputted and therefore,
(1) Before the toner replenishing device outputs the remaining amount detection signal, even if the measured value S is below the limit value L, the absence of the toner is not judged and therefore, even if the density of the developer in the developing device is temporarily sharply lowered by the continuous printing of high density images or the like, such wrong detection that in spite of the presence of the toner in the toner replenishing device, the absence of the toner is judged by mistake can be prevented; and
(2) Design is made such that the limit value L is made effective for the first time only after the toner replenishing device has outputted the remaining amount detection signal and therefore, it becomes possible to set the limit value L a little high, and the lowering of image density and the deterioration of the carrier due to the density of the developer having become too low can be prevented beforehand, and good images can be ensured till the last moment when the toner in the toner replenishing device becomes absent.
Accordingly, it is an object of the present invention to provide an image forming apparatus which can effect the detection of the absence of a toner and accident in a developing device provided with a toner replenishing device, without causing wrong detection and poor images.
The above object is achieved by the image forming apparatus according to the present invention. Summing up, the present invention is an image forming apparatus provided with at least one developing device having a developing container for containing therein a developer including a toner and a carrier, means for detecting the density of the developer in the developing container, and a toner replenishing device provided with a toner container containing the toner therein, and for replenishing the developing container with a proper amount of the toner in the toner container, wherein by the density of the developer in the developing container having become smaller than a predetermined limit value (L), it is judged that the developing container is not being replenished with the toner from the toner replenishing device, characterized in that the limit value (L) has a plurality of levels, and a value is selected and used in conformity with the remaining amount of toner in the toner container.
The present invention adopts the above-described construction, whereby before the toner replenishing device outputs a remaining amount detection signal, even if the measured value S is below the limit value L, the absence of the toner is not judged and therefore, even if the density of the developer in the developing container is temporarily sharply lowered by the continuous printing of high density images or the like, such wrong detection that in spite of the presence of the toner in the toner replenishing device, the absence of the toner is judged by mistake can be prevented. Also, design is made such that the limit value L is made effective for the first time only after the toner replenishing device has outputted the remaining amount detection signal and therefore, it becomes possible to set the limit value L a little high, and the lowering of image density and the deterioration of the carrier due to the density of the developer having becomes too low can be prevented beforehand, and good images can be ensured till the last moment when the toner in the toner replenishing device becomes absent.
Also, design is made such that different limit values L can be used properly in conformity with the remaining amount of toner in the toner container and therefore, it becomes possible to distinctively judge the absence of the toner in the toner container or the accident of the toner replenishing device or the like, and by effecting appropriate warning display, usability is greatly improved.
Thus, control partaking both of the accurate toner absence detection and inconvenience detection of the toner replenishing device can be realized by a simple construction.
According to the present invention, in an image forming apparatus provided with at least one developing device having a developing container for containing therein a developer including a toner and a carrier, means for detecting the density of the developer in the developing container, and a toner replenishing device provided with a toner container containing the toner therein, and for replenishing the developing container with a proper amount of the toner in the toner container, wherein by the density of the developer in the developing container having become smaller than a predetermined limit value (L), it is judged that the developing container is not being replenished with the toner from the toner replenishing device, design is made such that the limit value (L) has a plurality of levels, and a value is selected and used in conformity with the remaining amount of toner in the toner container and therefore,
(1) Before the toner replenishing device outputs a remaining amount detection signal, even if the measured value S is below the limit value L, the absence of the toner is not judged and therefore, even if the density of the developer is temporarily sharply lowered by the continuous printing of high density images or the like, such wrong detection that in spite of the presence of the toner in the toner replenishing device, the absence of the toner is judged by mistake can be prevented;
(2) Design is made such that the limit value is made effective for the first time after the toner replenishing device has outputted the remaining amount detection signal and therefore, it becomes possible to set the limit value a little high, and the lowering of image density and the deterioration of the carrier due to the density of the developer having become too low can be prevented beforehand, and good images can be ensured till the last moment when the toner in the toner replenishing device becomes absent;
(3) Design is made such that different limit values are used properly in conformity with the remaining amount of toner in the toner container and therefore, it becomes possible to distinctively judge the absence of the toner in the toner container or the accident of the toner replenishing device or the like, and by effecting appropriate warming display, usability is greatly improved; and
(4) Thus, control partaking both of the accurate detection of the absence of the toner and detection of the inconvenience of the toner replenishing device can be realized by a simple construction.
These and other objects, features, and advantages of the present invention will become more apparent upon consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.